Atherosclerotic disease is the major cause of death and disability in much of the world. Identifying genetic and environmental contributions to disease susceptibility is a current challenge requiring clinical and animal model studies. The creation of induced mutant mouse models susceptible to atherosclerosis has heralded a new era of research into the genetics of this disease. Not only can candidate genes be tested directly, but new genes and pathways can be identified by quantitative trait locus (QTL) mapping. In crosses betweenC57BL/6J and FVB/N mice on the apo E knockout background, a very strong proximal chromosome 10 atherosclerosis susceptibility locus was identified. Unexpectedly, the genotypic means for aortic root lesion area for markers at this locus indicated homozygosity for the FVB/N allele was associated with increased atherosclerosis compared to heterozygosity and homozygosity for the C57BL/6J allele. This finding was confirmed by characterizing congenic lines encompassing the 0 to 21.9cM region. Now, eight subcongenic lines have also been characterized and it appears the locus is complex with one gene between 11.4 and 19.6 Mb (10a) and another between 20.0 and 22.3 Mb (10b). A promising candidate gene in the 10a region, named A20, has been studied. A20 is a gene turned on by the TNFa/NFkB pathway, which then acts to shut down signaling through the pathway. C57BL76J and FVB/N A20 were shown to differ at a single codon and after TNFa stimulation FVB/N A20 was much more effective at shutting down the TNFa/NFkB pathway than C57BL/6J A20. The TNFa/NFkB pathway is both proinflammatory and antiapoptotic and could influence atherosclerosis by either mechanism. The specific aims of this proposal are to identify the causal genes in the 10a and 10b regions by further defining the critical intervals with additional subcongenic lines, sequencing and expression analysis of genes within these intervals, and the creation of induced mutant mouse lines for promising genes to prove causation. In addition, the role of A20 in atherosclerosis will be further explored in induced mutant mice and mechanistic studies will be carried out in whole animal and tissue culture studies. Particular attention will be paid to how the functional difference between C57BL/6J and FVBV/N A20 may act to alter the balance between TNFa mediated inflammation and apoptosis and how this might affect atherosclerosis progression. We anticipate that these studies will shed light on new genes and pathways that control atherosclerosis susceptibility, which may lead to improved diagnosis of susceptible individuals in the population, and someday to novel mechanism based therapies.